Magnetic transducer



Nov. 17, 1959 w. A. HOLMAN MAGNETIC TRANSDUCER Filed Dec 28. 11953 FIG. 1

FIG.3

IN V EN TOR.

, h6: /0 A. Ha/ma n United States Patent O MAGNETIC TRANSDUCER Wesley A. Holman, Los Gatos, Califi, assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Application December 28, 1953, Serial No. 400,543

4 Claims. (Cl. 179- 1002) The present invention appertains generally-to magnetic transducers and relates more particularly to cores for such transducers.

When assembling magnetic recording heads, there are two plausible methods of placing the coil on the core. One method is to manufacture the core in two pieces. The coil is placed on one core piece and, by skillful use of a special jig, the other core piece is carefully cemented or soldered in place. The disadvantages of this method are several. Firstly, the manufacturing costs are increased due to the painstaking workmanship and special equipment which are necessary to properly assemble the core, and secondly, when the core is made in two pieces, there results an extra gap in the magnetic path, which gap increases the reluctance of the core, thereby reducing the efliciency of the recording head. This is true, no matter how carefully the two core pieces are affixed to each other. The second method is to use a one piece core, to then bend a leg thereof sufiiciently to permit insertion of the coil on the core, and finally to bend the core leg back to its normal position. This second method is generally preferred, inasmuch as it is less expensive. However, it should be noted that the sharp bend normally necessary for the insertion of the coil increases the reluctance of that portion of the core strained by the bending, the increase in reluctance being directly proportional to the degree of bend, and thereby decreases the efficiency of the core.

One object of this invention is to provide an improved magnetic transducer.

Another object is to provide a transducer core wherein the effect of the bending which is necessitated by the insertion of the coil is minimized.

When the physical size of a recording head is to be minimized, by making the cross-sectional area of the core as small as possible, it is highly important to obtain a core having a maximum efiiciency, i.e., having a minimum reluctance per unit of cross-sectional area.

It is another object of this invention, therefore, to provide a transducer core having a maximum efiiciency.

Another object is to provide a transducer wherein the danger of damage to the parts thereof is minimized.

These and other objects and advantages will become apparent from the following description and accompanying drawings, in which:

Fig. 1 is a partial section taken along line 11 of Fig. 2.

Fig. 2 is a bottom view of the recording head of the invention.

Fig. 3 is a diagrammatic view of the head encased in a protective sheath.

The recording head of the present invention comprises a substantially rectangular, paramagnetic core 10. Provided in the core 10, near one end 11 thereof, is a coil receiving slot 12.. The slot 12 is arranged longitudinally of the core to receive therethrough a flat pancake type coil 13 which is mounted on a vertically disposed toe 14 of one leg 15 of the core 10. The core is formed 2,913,535 Patented Nov. 17, 1959 1 with the usual high reluctance gap 16, extending from the in Fig. 1.

lower surface 17 of the core 10 to the slot 12, and a narrow slit 18 in the core 10 is arranged to extend from the slot 12, parallel to the longitudinal axis of the core, toward the other end 19 thereof, substantially as shown Additionally, it should be noted that the slit 18 is arranged to merge with the slot 12 above the lower extremity thereof, to thereby provide the other leg 20 of the core 10 with a length, indicated at A, which is wider, and thereby has a greater cross-sectional area,

than that portion of the leg indicated at B.

When, during assembly of the head, the coil 13 is to be mounted on the core 10 in the position shown in the drawings, the leg 20 of the core is deformed and moved to the position shown in phantom lines in Fig. 2 to there by permit insertion of the coil in the slot 12. With the coil 13 in place, the leg 20 is then returned to the normal position shown in full lines in Fig. 2. Though not shown in the drawings, the leg 20 may be secured to the toe 14 with a high reluctance material, such as silver solder, to provide and maintain the gap 16 with the desired dimensions as well as to furnish rigidity to the core structure.

As will become clear hereinafter, it is preferred to con fine the bending of the leg 20 to that portion thereof which is defined by A, as opposed to B, i.e., that portion which has the larger cross-sectional area. The purpose of the slit 18 and of its location in the core is two-fold. First, the slit provides an increased bending radius for the leg 20, and, since the reluctance varies directly with the degree of bend, the effect of bending upon the reluctance of the core is decreased, thereby maintaining the increase in the reluctance due to bending at a minimum. Second, since reluctance is inversely proportional to the cross-sectional area, the increased cross-sectional area at A minimizes the effect of the increased reluctance due to the bending which takes place in section A.

It should be clear, therefore, that by the provision of the novel arrangement of the slit 18 in the core 10 and by providing an increased cross-sectional area of that portion of the core which is bent, the efficiency of the core is maintained at a maximum.

In a preferred embodiment of the invention (Fig. 3) the transducer is embedded in a protective sheath 23, of plastic or the like, to prevent deformation of and/or damage to the core and coil parts. Leads 24 of the coil 13 may extend from the sheath 23, as at 22, for connection to a suitable operating mechanism (not shown).

While there have been shown, described and pointed out the fundamental novel features of the invention as applied to its use in magnetic recording heads, it will be understood that various omissions, substitutions and changes in the form and details of the device illustrated may be made by those skilled in the art without departing from the spirit and scope of the invention. It is the intention, therefore, to be limited only as indicated in the following claims.

What I claim is:

1. A magnetic transducer comprising a core having first and second leg members joined integrally at one end and extending therefrom to define in succession a relatively narrow slot, a coil receiving window merging with said slot and a gap merging with said window and defined by the distal ends of said members, the narrow dimension of said slot being substantially less than the narrow dimension of said window, and a preformed pancake type winding surrounding one of said distal ends and substantially filling said window.

2. A magnetic transducer comprising a core including a body having first and second leg members joined integrally at one end and spaced apart at the other end to define a gap for interrupting the magnetic continuity of the magnetic circuit defined by said members, portions of said leg members intermediately of said one end and said gap defining a rectangular coil receiving window, a slot extending from said window to said one end parallel to the long dimension of said rectangular window, said-portions adjacent said slot having a cross-sectional area larger than the cross-sectional area of the portions adjacent said Window, and a preformed pancake type Winding surrounding said other end, said Winding having a cross section corresponding in size to said window.

3. A magnetic transducer comprising a core member and winding means, said core member having a pair of leg members joined integrally at one end and extending therefrom to define in succession a relatively narrow slot, a Window for receiving said Winding means and a gap, the narrow dimension of said slot being substantially 15 2,702,835

7 4 less than the narrow dimension of said window, said winding means comprising a pancake type coil having a radially extending cross section which corresponds substantially to said window.

4. The invention set forth in claim 3 wherein the portions of the leg members adjacent said slot have a greater cross-sectional area than the portions of said members adjacent said window.

Rettinger Feb. l0, 1953 Field Nov. 24, 1953 Camras Feb. 22, 1955 

